Add GetExpirationTimes() to HttpResponseHeader.

net/http/http_response_headers.cc

Index: net/http/http_response_headers.cc
diff --git a/net/http/http_response_headers.cc b/net/http/http_response_headers.cc
index b45012569c67fe6c5bbc45551a30df6465dd877b..e96b8cd7f1afec1d4e25a499525f42ed429a4e06 100644
--- a/net/http/http_response_headers.cc
+++ b/net/http/http_response_headers.cc
@@ -905,18 +905,32 @@ bool HttpResponseHeaders::IsRedirectResponseCode(int response_code) {
 //
 //   response_is_fresh = (freshness_lifetime > current_age)
 //
+// Into this equation, we substitute |current_age = now - freshness_origin|,
+// giving:
+//
+//   response_is_fresh = (freshness_lifetime > now - freshness_origin)
+//
+//   response_is_fresh = (freshness_lifetime + freshness_origin > now)
+//
+// And we call this quantity |freshness_lifetime + freshness_origin| the
+// freshness_expiry.
+//
 // Of course, there are other factors that can force a response to always be
 // validated or re-fetched.
 //
-bool HttpResponseHeaders::RequiresValidation(const Time& request_time,
-                                             const Time& response_time,
-                                             const Time& current_time) const {
-  TimeDelta lifetime =
-      GetFreshnessLifetime(response_time);
-  if (lifetime == TimeDelta())
-    return true;
+Time HttpResponseHeaders::GetFreshnessExpiry(Time request_time,
+                                             Time response_time) const {
+  TimeDelta lifetime =  GetFreshnessLifetime(response_time);
+  if (lifetime.is_max())
+    return Time::Max();
+  Time origin = GetFreshnessOrigin(request_time, response_time);
+  return origin + lifetime;
+}
 
-  return lifetime <= GetCurrentAge(request_time, response_time, current_time);
+bool HttpResponseHeaders::RequiresValidation(base::Time request_time,

[gavinp, 2014/02/13 18:50:26]

s/base::Time/Time/

+                                             base::Time response_time,
+                                             base::Time current_time) const {
+  return GetFreshnessExpiry(request_time, response_time) <= current_time;
 }
 
 // From RFC 2616 section 13.2.4:
@@ -939,8 +953,7 @@ bool HttpResponseHeaders::RequiresValidation(const Time& request_time,
 //
 //   freshness_lifetime = (date_value - last_modified_value) * 0.10
 //
-TimeDelta HttpResponseHeaders::GetFreshnessLifetime(
-    const Time& response_time) const {
+TimeDelta HttpResponseHeaders::GetFreshnessLifetime(Time response_time) const {
   // Check for headers that force a response to never be fresh.  For backwards
   // compat, we treat "Pragma: no-cache" as a synonym for "Cache-Control:
   // no-cache" even though RFC 2616 does not specify it.
@@ -1040,9 +1053,15 @@ TimeDelta HttpResponseHeaders::GetFreshnessLifetime(
 //   resident_time = now - response_time;
 //   current_age   = corrected_initial_age + resident_time;
 //
-TimeDelta HttpResponseHeaders::GetCurrentAge(const Time& request_time,
-                                             const Time& response_time,
-                                             const Time& current_time) const {
+// From this, we can derive the freshness origin, the time at which the
+// current_age = 0 and solve for now (aka freshness_origin):
+//
+//   corrected_initial_age + resident_time = 0
+//   corrected_initial_age + freshness_origin - response_time = 0
+//   freshness_origin = response_time - corrected_initial_age
+//
+Time HttpResponseHeaders::GetFreshnessOrigin(Time request_time,
+                                             Time response_time) const {
   // If there is no Date header, then assume that the server response was
   // generated at the time when we received the response.
   Time date_value;
@@ -1058,10 +1077,8 @@ TimeDelta HttpResponseHeaders::GetCurrentAge(const Time& request_time,
   TimeDelta corrected_received_age = std::max(apparent_age, age_value);
   TimeDelta response_delay = response_time - request_time;
   TimeDelta corrected_initial_age = corrected_received_age + response_delay;
-  TimeDelta resident_time = current_time - response_time;
-  TimeDelta current_age = corrected_initial_age + resident_time;
 
-  return current_age;
+  return response_time - corrected_initial_age;
 }
 
 bool HttpResponseHeaders::GetMaxAgeValue(TimeDelta* result) const {